The versatility and economics of flexible cellular foamed polyurethane materials (referred to as “polyurethane foams”) have resulted in their adaptation for variety of uses including furniture cushioning, carpet underlayment, and cosmetic and medical applications such as absorbent wound dressings. In such application, it is desirable that dressings remain in place for several days to absorb the wound exudate and to minimize dressing changes to reduce the risk of trauma to the healing wound. It is also desirable that such foam wound dressings not support micro-organism growth but aid in lowering the bio-burden. Thus, antimicrobial properties are very much desired in the foam material used in wound care applications.
There are several antimicrobial foam dressings in the market. Examples include PolyMem®, an antimicrobial foam dressing and Bio-Patch®, an antimicrobial site dressing. Silver is the active in the PolyMem® product and an organic compound is the active in the Bio-Patch® product. Considering the fact silver is a broad spectrum antimicrobial and has been widely incorporated in a variety of wound care products, introducing silver into foam products has proved somewhat challenging. The difficulty of incorporating silver chemistries in foam products stems from its susceptibility to chemical reduction to metallic silver in the presence of polyurethane precursors. Post reduction, the presence of metallic silver imparts black or brown color to the foam such is the case with PolyMem® foam dressing.
In advancing the art, PCT International Publication WO 2004/007595 A1 by Lendell et al. for “Antimicrobial Polyurethane Foam” describes flexible polyurethane foam (i.e., foamed polyurethane) that incorporates a silver-based antimicrobial agent in the form of silver sodium hydrogen zirconium phosphate available as Antimicrobial AlphaSan® from Milliken Chemical of Spartanburg, S.C. This material may be mixed in with a polyisocyanate (i.e., multi-functional isocyanate) component or a polyol component (or both) prior to reaction.
One disadvantage with silver sodium hydrogen zirconium phosphate is that silver is not readily available for antimicrobial action. A large amount of the active agent is required to ensure a minimum efficacy threshold and to sustain long duration activity thus adding to the cost.
Accordingly, there is a need for improved antimicrobial polyurethane foam products. For example, there is a need for flexible cellular polyurethane foam products and flexible cellular hydrophilic polyurethane foam products that resist discoloration. This need extends to antimicrobial polyurethane foam products incorporating metal-based antimicrobial compositions. There is also a need for antimicrobial polyurethane foam products having a uniform distribution of metal-based antimicrobial compositions that resist discoloration.